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Front. Physiol. | doi: 10.3389/fphys.2018.01831

Pharmacological modulation of mitochondrial Ca2+ content regulates sarcoplasmic reticulum Ca2+ release via oxidation of the ryanodine receptor by mitochondria-derived reactive oxygen species.

 Shanna Hamilton1, 2,  Radmila Terentyeva2,  Tae Yun Kim1, 2,  Peter Bronk2,  Jin O-Uchi3, György Csordás4, Bum-Rak Choi1, 2 and  Dmitry Terentyev1, 2*
  • 1Brown University, United States
  • 2Rhode Island Hospital, United States
  • 3University of Minnesota Twin Cities, United States
  • 4Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, United States

In a physiological setting, mitochondria increase oxidative phosphorylation during periods of stress to meet increased metabolic demand. This in part is mediated via enhanced mitochondrial Ca2+ uptake, an important regulator of cellular ATP homeostasis. In a pathophysiological setting pharmacological modulation of mitochondrial Ca2+ uptake or retention has been suggested as a therapeutic strategy to improve metabolic homeostasis or attenuate Ca2+-dependent arrhythmias in cardiac disease states. To explore the consequences of mitochondrial Ca2+ accumulation, we tested the effects of kaempferol, an activator of mitochondrial Ca2+ uniporter (MCU), CGP-37157, an inhibitor of mitochondrial Na+/Ca2+ exchanger, and MCU inhibitor Ru360 in rat ventricular myocytes (VMs) from control rats and rats with hypertrophy induced by thoracic aortic banding (TAB).
In periodically paced VMs under β-adrenergic stimulation, treatment with kaempferol (10 μmol/L) or CGP-37157 (1 μmol/L) enhanced mitochondrial Ca2+ accumulation monitored by mitochondrial-targeted Ca2+ biosensor mtRCamp1h. Experiments with mitochondrial membrane potential-sensitive dye TMRM revealed this was accompanied by depolarization of the mitochondrial matrix. Using redox-sensitive ERroGFP_iE biosensor, we found treatment with kaempferol or CGP-37157 increased the levels of reactive oxygen species (ROS) in the sarcoplasmic reticulum (SR). Confocal Ca2+ imaging showed that accelerated Ca2+ accumulation reduced Ca2+ transient amplitude and promoted generation of spontaneous Ca2+ waves in VMs paced under ISO, suggestive of abnormally high activity of the SR Ca2+ release channel ryanodine receptor (RyR). Western blot analyses showed increased RyR oxidation after treatment with kaempferol or CGP-37157 vs controls. Furthermore, in freshly isolated TAB VMs, confocal Ca2+ imaging demonstrated that enhancement of mito-Ca2+ accumulation further perturbed global Ca2+ handling, increasing the number of cells exhibiting spontaneous Ca2+ waves, shortening RyR refractoriness and decreasing SR Ca2+ content. In ex vivo optically mapped TAB hearts, kaempferol exacerbated proarrhythmic phenotype. On the contrary, incubation of cells with MCU inhibitor Ru360 (2 μmol/L, 30 min) improved intracellular Ca2+ homeostasis and reduced triggered activity in ex vivo TAB hearts.
These findings suggest facilitation of mitochondrial Ca2+ uptake in cardiac disease can exacerbate proarrhythmic disturbances in Ca2+ homeostasis via ROS and enhanced activity of oxidized RyRs, while strategies to reduce mitochondrial Ca2+ accumulation can be protective.

Keywords: Mitochondria, Reactive Oxygen Species, Ryanodine receptor (RyR), Hypertrophy, ventricular arrhythmia, calcium-induced calcium release

Received: 21 Sep 2018; Accepted: 06 Dec 2018.

Edited by:

Angélica Rueda, Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico

Reviewed by:

José J. López Barba, Universidad de Extremadura, Spain
Diego De Stefani, Università degli Studi di Padova, Italy  

Copyright: © 2018 Hamilton, Terentyeva, Kim, Bronk, O-Uchi, Csordás, Choi and Terentyev. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Dmitry Terentyev, Brown University, Providence, United States, dmitry_terentyev@brown.edu